Intraoperative neurophysiological monitoring (IONM), which refers to the intraoperative use of neurophysiological studies for the functional assessment of neural networks and monitoring of neural integrity during surgery, was introduced in South Korea in the 1990s. However, its use did not become widespread until the 2010s when the Korean National Health Insurance Service (KNHIS) started to cover it, and with the development of a novel modality. In response to the growing popularity of IONM, which is now also a global phenomenon, the Korean Society of Clinical Neurophysiology revised its neurophysiological testing guidelines to include IONM content. The rapidly changing medical landscape both domestically and outside South Korea has necessitated the development of a more practical set of IONM guidelines.

Numerous studies on IONM have been reported, and especially in the official journal of the Korean Society of Intraoperative Neurophysiological Monitoring: the Journal of Intraoperative Neurophysiology. However, these studies do not completely encompass the recent rapid changes in the field of IONM. Accordingly, an IONM quality-management task force was formed to develop the present clinical practice guidelines, which have been tailored to the current IONM conditions in South Korea. These guidelines explain the principles and rationale of IONM together with its supervision, and proposes several recommendations for performing the recently developed diverse IONM techniques.

The goal of IONM is either the early detection of intraoperative nerve damage or the precise localization of major nerves that are susceptible to intraoperative damage, thereby minimizing the risk of postoperative neurological deficits. Toward that goal, IONM involves monitoring of neural pathways, cerebral blood flow, and the level of neural function during surgery. This not only ensures the safety of patients, but also helps them, their legal guardians, and their medical team to confidently approach the surgery, especially if that surgery is particularly technically challenging.

IONM uses diverse neurophysiological testing techniques that have been developed to diagnose patients with neurological disorders. The types of neurophysiological testing that have been adapted for IONM include motor evoked potentials (MEPs) for monitoring the descending motor pathways, somatosensory evoked potentials (SSEPs) for ascending sensory pathways, brain auditory evoked potentials (BAEPs), visual evoked potentials (VEPs), and electroencephalography (EEG) for recording the electrical activity of the brain, and electromyography (EMG) for monitoring peripheral neuromuscular systems. Transcranial Doppler (TCD), which is a type of ultrasonography, can also be used. Among these diverse modalities, appropriate tests of choice can be chosen according to the particular type of surgery and its inherent risks.

In principle, IONM can be used for all surgical procedures for which there is a risk of intraoperative neural damage. However, it is generally only implemented for surgeries with a high risk of postoperative neural deficit or for which evidence-based efficacy of IONM has been demonstrated. These surgeries include functional neurosurgery, such as brain or cerebral nerve surgery, cerebrovascular surgery, epilepsy surgery, and various types of spine and spinal-cord surgery. In general, the involved IONM neurophysiologist will discuss the planned surgery with the surgeon ahead of time to agree upon the most appropriate IONM modalities.

The development and advancements in monitoring devices have expanded the target surgical procedures for which IONM can be implemented. At each institution, the IONM modalities and their settings should be decided for the target surgical procedure at the discretion of the neurophysiologist and with the cooperation of the anesthesiologist and surgeon.

It is essential that the IONM team includes neurophysiologists, operating surgeons, anesthesiologists, and medical technologists. A close interaction between these members is required for precise and successful IONM.¹

The neurophysiologist is responsible for the overall management of IONM, including the choice of IONM equipment, settings, and monitoring method for each case, and for determining the level of monitoring that will be required, interpreting IONM results, and educating the monitoring technologist.² As a supervising physician, the neurophysiologist should be familiar with a wide range of monitoring techniques, know which is the most appropriate to obtain the required waveforms during a particular type of surgery, recognize the meaning behind any changes in those waveforms and be able to reduce any artifacts, and be able to supervise and guide the medical technologist in the performance of these monitoring techniques. In this setting, neurophysiologists should also be able to not only properly and clearly report waveforms or waveform changes observed on a monitor to the operating surgeon, but should also be able to interpret their clinical significance. They should not only have a good understanding of neurophysiology, but should also have received full-time training on the methods of electrophysiological testing including generation of evoked potentials (EPs), EMG, EEG, nerve conduction studies (NCS), and ultrasonography. In South Korea, board-certified neurologists or rehabilitation medicine physicians would qualify as neurophysiologists based on the training that they receive.

A medical technologist is defined by Korean domestic laws as a professional who is supervised by a physician or a dentist and is responsible for performing chemical or physiological tests. As a member of an IONM team, the medical technologist performs neurophysiological tests in the operating room. IONM does not refer to a specific type of test, but rather to the comprehensive use of a collection of various clinical neurophysiological tests such as generating EPs, EMG, EEG, NCS, and TCD. Simply knowing how to use IONM equipment or having the ability to interpret IONM waveforms does not necessarily indicate that the neurophysiologist has received sufficient training to perform optimal IONM.

While a full IONM team consisting of at least four members- an operating surgeon, an anesthesiologist, a neurophysiologist, and a medical technologist trained by a neurophysiologist-is usually necessary to perform IONM, a smaller team may suffice under limited circumstances. For instance, a single operating surgeon with a single anesthesiologist may be sufficient for thyroid surgery, whereby the operating surgeon locates the recurrent laryngeal nerve using an automated device, performs vagus nerve stimulation, and uses a device that records vocal-cord movements from recording electrodes and converts the generated EMG signals into sounds. However, the IONM process as performed by a small number of medical professionals should differ from that performed by a complete team in terms of its purpose and accuracy, and therefore should not be considered equivalent. Furthermore, alarm sounds or simple verbal communication about any waveform changes are not recommended for interpreting waveforms in IONM if they are not accompanied by the interpretation of the waveforms observed on a monitor. A neurophysiologist who can perform and supervise IONM and a medical technologist certified in neurophysiology are essential members of an IONM team. It is recommended that these personnel cooperate with the operating surgeon and anesthesiologist as part of an integrated IONM team.

Defining the required level of supervision by a clinical neurophysiologist during IONM is important, and is summarized as below based on recommendations from medical communities in foreign countries and textbooks on IONM.

Supervision of medical technologists by a neurophysiologist during IONM is classified as direct, personal, or general depending on the purpose and method of supervision. Among these, direct supervision is the most commonly used during IONM according to current KNHIS requirements. In performing direct supervision, a neurophysiologist should be available close to the operating surgeon or medical technologist to provide supervision when needed, or should provide online supervision in real time. The potential for direct online supervision is currently increasing due to recent advances in communication technology and devices. In South Korea, direct online supervision is provided during IONM for most surgical procedures involving the brain, spine, spinal cord, and blood vessels. In general, routine tests performed in a laboratory (e.g., MEPs and SSEPs) are repeated to monitor waveform changes, and the test results are objectively represented as numbers or waveforms changes. Most textbooks as well as domestic and foreign recommendations state that IONM does not require a neurophysiologist to remain in the operating room throughout the surgery. For example, the coverage policies recently revised by the American Academy of Neurology state that supervision is performed either in the operating room or via a real-time connection outside the operating room.³ Therefore, it is sufficient for a neurophysiologist to perform real-time monitoring close to the operating room (usually within the same building where the surgery is taking place or somewhere nearby) via a wired (local area network or optical cable) or wireless connection, and provide immediate supervision to a medical technician when major changes in waveforms occur The neurophysiologist is responsible for interpreting the waveform changes, and enters the operating room only when necessary.^4-8

Personal supervision is provided for IONM that includes brain stimulation and cognitive tests such as assessment of the language and motor regions of the brain for brain tumor or epilepsy surgery. These require high levels of professional knowledge and experience. It is recommended that a medical technologist performs IONM under the personal supervision of a neurophysiologist.^4-6 However, extensive discussions on the testing method and interpretation of the results, as well as communication between the operating surgeon and the neurophysiologist are necessary before performing IONM that requires personal supervision. The medical cost for personal supervision during IONM is not currently specified by the KNHIS. General supervision is provided by a neurophysiologist in the absence of direct or personal supervision of a neurophysiologist.

While IONM is performed simultaneously and in the same space as the surgery and anesthesia, it remains distinct from both. Therefore, in countries including the United States, neither the surgeon nor the anesthesiologist performing a surgical procedure can bill for IONM since it is included in the global package when serving as the physician supervising IONM.³ It is not advisable for a neurophysiologist to provide direct supervision for IONM performed on an outpatient basis. Given that neurophysiologists in South Korea are also responsible for providing outpatient services in departments of neurology or rehabilitation medicine, it is recommended that each institution has at least two neurophysiologists to allow IONM to be performed continuously. It is also recommended that neurophysiologists maintain appropriate levels of supervision with respect to both the patient and the surgical procedure during IONM.

When an alarm sound alerts to the possibility of nerve damage during surgery, the clinical neurophysiologist and medical technologist should quickly investigate whether the IONM device is functioning properly, check for artifacts, and check for changes in the anesthetic agents or the patient’s general condition (blood pressure, body temperature, oxygen saturation level, electrolyte levels). If none of these are observed, they should inform the operating surgeon of the possibility of intraoperative nerve damage.

TCD may be used to check for any disruption in the cerebral blood flow based on a reduction in systolic blood flow. High-intensity transient signals generated by emboli as well as high-pitched sound signals may also be used to assess cerebral blood flow.The billing for IONM depends upon the duration of testing, and therefore precise recording of the testing time is important. Both the recording time and testing time are usually referred to in the billing process for IONM (Fig. 1). The recording time refers to the time from the start of recording of baseline waveforms to when the closing data are obtained. The testing time refers to the time from the start of test preparation, including setting up the equipment and placing the electrodes and stimulator, to the time when the IONM process, including electrode removal/disposal, patient examination, and saving of data, is complete. Billing IONM based on the test time is most appropriate since IONM starts before and continues after data collection.

Documentation of data interpretation should show the basic information, the modality of monitoring, the monitoring results, and the conclusions, and may include additional comments if needed. The basic information includes the date of the test, and the patient’s name, sex, age, and registration number. It should also include details about the surgery itself, including the type of surgery, the surgical site, and the name of the operating surgeon, as well as information about the anesthetic procedure, including the type of anesthetic procedure, doses of anesthetic agents, and the names of the anesthesiologist, medical technologist, and neurophysiologist. It is recommended that the monitoring and recording times be indicated clearly when documenting the basic information, in order to facilitate the insurance claims process (Fig. 2).

These guidelines include useful recommendations that are supported by currently available clinical evidence. They provide explanations of the basic principles, indications, team composition, levels of supervision, precautions, and equipment, including electrodes and other devices for IONM. Moreover, a summary of current monitoring techniques, methods for interpreting and documenting IONM results and recording the testing time, and principles of IONM interpretation are described. Finally, these guidelines provide an in-depth summary of the different levels of supervision, testing times, and methods of IONM data interpretation in relation to KNHIS coverage.